It is a story collection. Egan wrote one of my favorite-ever sci-fi stories: "Reasons to be Cheerful". But for some reason I never sought out a collection by him until now. I think this collection is fantastic. Greg Egan gets a bad rap as one of those writers who is full of great ideas but is short on characterization. But that is not correct! In fact it is the opposite of correct! His virtue is actually that he ties great ideas to really human stories. He manages to extract all the natural emotion from his premises, and it's honestly pretty amazing. Only read the first three stories now, but the second one--"The Hundred Light-Year Diary"--is a tour de force. It takes place in a world where people are able--as a matter of course--to send back their daily observations (their daily diary) to their past selves. Basically, from the age of twelve onwards, the main character knows exactly what is going to happen to him.
The story, though, starts on the day that he meets the love of his life. And even though he does fall for her, and he does feel for her, there's still something subtly wrong about the experience. And as the story progresses, it not only brings up the usual questions about free will, but it also manages to bring out the thematic resonances: the ways in which this premise raises natural questions about growing up and aging and our moral responsibility to the world. Just a fantastic, fantastic story.